Castro Valley, California climate: NOAA's gridded normals for the city, beside the nearest station records
NOAA's gridded 1991-2020 normals put Castro Valley's center at January lows of 40°F and July highs of 82°F, a yearly mean of 59.6°F and 19.7 inches of precipitation. No NOAA station keeps a record under the city's name. The nearest station record, Hayward (5 miles SW, 43 ft), has January lows of 43°F and July highs of 75°F.
65,389 people (Census Bureau 2024). Distances and directions are from the city's center.
- Jan 58° 40°
- Feb 62° 43°
- Mar 65° 45°
- Apr 69° 46°
- May 74° 50°
- Jun 80° 53°
- Jul 82° 56°
- Aug 82° 56°
- Sep 82° 54°
- Oct 76° 51°
- Nov 65° 44°
- Dec 58° 40°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
The months above are NOAA's gridded normals at Castro Valley's center.
What is each month like in Castro Valley?
NOAA's grid estimates the normals every 5 km or so from the stations around each point, terrain included. It smooths between stations, so night lows at the heart of a large city can run warmer than the grid shows: at five big-city airports we compared, the grid's highs were within about 1°F of the station and its lows 1-6°F cooler. The nearest record's high and low are beside each month.
| Month | High | Low | Mean | Precip. | Hayward high | Hayward low |
|---|---|---|---|---|---|---|
| January | 58°F | 40°F | 49.1°F | 3.75 | 59°F | 43°F |
| February | 62°F | 43°F | 52.1°F | 3.71 | 62°F | 45°F |
| March | 65°F | 45°F | 54.9°F | 2.90 | 64°F | 47°F |
| April | 69°F | 46°F | 57.5°F | 1.51 | 67°F | 50°F |
| May | 74°F | 50°F | 61.6°F | 0.72 | 69°F | 52°F |
| June | 80°F | 53°F | 66.5°F | 0.15 | 74°F | 55°F |
| July | 82°F | 56°F | 69.0°F | 0.00 | 75°F | 57°F |
| August | 82°F | 56°F | 69.2°F | 0.04 | 76°F | 58°F |
| September | 82°F | 54°F | 67.9°F | 0.11 | 77°F | 58°F |
| October | 76°F | 51°F | 63.2°F | 0.93 | 74°F | 54°F |
| November | 65°F | 44°F | 54.8°F | 2.04 | 65°F | 47°F |
| December | 58°F | 40°F | 49.0°F | 3.89 | 59°F | 43°F |
In metric: a yearly mean of 15.3°C, January lows of 5°C, July highs of 28°C and 501 mm of precipitation a year.
Source: NOAA NCEI U.S. Monthly Gridded Climate Normals 1991-2020 (nClimGrid, accession 0245564); NOAA NCEI 1991-2020 station normals. The grid cell holding the city's Census center point.
What do the station records around Castro Valley say?
Each row is a NOAA station's own 1991-2020 normals, with the snow and frost dates the grid does not give. A record downhill or nearer the coast than the city can run warmer, one uphill cooler: compare the elevations.
| Record | Where | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| HaywardHayward Air Terminal | 5 mi SW | 43 ft | 59.6°F | 43°F | 75°F | 16.0 | – | January 2 |
| OaklandOakland Metro International Airport | 9 mi W | 6 ft | 58.1°F | 42°F | 72°F | 18.7 | – | January 7 |
| Fremont | 12 mi S | 38 ft | 59.5°F | 43°F | 78°F | 15.9 | 0 | January 7 |
Source: NOAA NCEI 1991-2020 U.S. Climate Normals; place center and population: Census Bureau 2024. Last frost: the median last spring date of 32°F.
How much snow, how late a frost, what zone and how much sun in Castro Valley?
NOAA's grid gives no snow, frost dates or records, so these come from the nearest station record, Hayward (5 miles SW, 43 ft). NOAA publishes no snowfall normal for it; the nearest record that has one, Fremont (12 miles S), gets 0 inches a year. The last spring frost (32°F) comes after January 2 in half of years and the first autumn frost before December 25. Its record high is 108°F (2017) and its record low 27°F (1998) (kept since 1998).
The USDA's 2023 Plant Hardiness Zone Map puts Castro Valley in zones 9b to 10a across its 3 ZIP code areas.
Over a year 80% of the sunlight that would reach the ground under clear skies gets through the clouds in the area (4.7 kWh per square metre a day, NASA POWER 2001-2020); June is the sunniest month (84%) and December the cloudiest (74%).
Hayward's page has its months, frost probabilities, records by month and recent years. NOAA's grid has monthly figures only, so there are no day-by-day month pages for Castro Valley; the nearest record's month pages have them.
Source: NOAA NCEI 1991-2020 normals, station USW00093228; records: ACIS; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; sunshine: NASA POWER.
How does the climate vary across Castro Valley, ZIP code by ZIP code?
3 ZIP code areas lie wholly or partly in Castro Valley. On NOAA's grid 94552 is the warmest (59.5°F a year) and 94546 the coolest (59.2°F), so the city is nearly uniform. Each row also names the nearest station record and its frost dates.
| ZIP code | Zone | Year | Jan low | Jul high | Precip. | Nearest record | Last frost | First frost |
|---|---|---|---|---|---|---|---|---|
| 94546 | 9b | 59.2°F | 41°F | 81°F | 20.3 | Hayward (6 mi) | January 2 | December 25 |
| 94552 | 9b | 59.5°F | 41°F | 83°F | 22.4 | Hayward (7 mi) | January 2 | December 25 |
| 94578 | 10a | 59.3°F | 44°F | 75°F | 18.2 | Hayward (4 mi) | January 2 | December 25 |
Source: Census Bureau 2020 ZCTA-to-place relationship file and ZCTA centers; NOAA NCEI gridded and station normals, 1991-2020. A ZIP area counts when at least a tenth of its land (and 0.5 km²) is in the city; its figures are the grid cell at its center; frost dates are the nearest record's medians of 32°F.